This invention relates to deicing agents, and more particularly, it is related to a deicing composition comprising an alkali metal or alkaline earth metal chloride, saccharinic acid and lignosulfonate.
In winter months the presence of snow and ice on roads, sidewalks, bridges, airport runways and highways presents serious safety hazards and operational difficulties that hinder everyday activities such as driving, walking, flying and so on. Over the years, many methods have been used in the colder regions of the world to remove or destroy ice or snow. The ice-removal process (or deicing) includes certain techniques ranging from simple approaches such as shoveling or plowing, to heating by means of buried heating elements or by the direct application of heat, to chemical methods i.e. the use of deicing chemicals such as sodium chloride and calcium chloride. For an effective treatment of large surface areas such as roads and runways, a combination of mechanical deicing (snowplowing) and chemical deicing (salt and sand) is normally employed.
The most commonly used chemical deicer for highways is rock salt i.e. sodium chloride. Rock salt is inexpensive and readily available in large quantities. Calcium chloride and magnesium chloride are sometimes used for their higher deicing power. However, the calcium and magnesium salts are substantially more expensive and magnesium chloride is more corrosive than rock salt, thus limiting their use. At the present time, it is estimated that the usage of rock salt in the U.S.A. alone amounts to 9 to 10 million tons per year for deicing applications.
Several disadvantages of using deicing salts have been experienced. These are for example salt contamination of ground water, damage to vegetation, and corrosion of vehicles and highway appurtenances. Chlorides dissolve readily in water and are known to accelerate the corrosion rate of metals. In a report entitled "Sprinkle Lightly - Salt And Alternatives For Highway De-Icing", Canadian Government Report No. MSP-4-01, published by the Ontario Ministry of Transportation and Communications, it was found that in the Toronto area 50% of the corrosion occurring on auto body steel was due to salt use during the winter months. Deicing salt also contributes to the corrosion of reinforcing steel in concrete bridge decks and substructures which would otherwise be protected by the alkaline environment in concrete.
In recent years, increased attention has been focused on alternative methods of deicing roadways. There are now available various ways of reducing the corrosive effects of salt. One alternative to salt is calcium magnesium acetate (CMA). Tests so far suggest that CMA is less polluting and less corrosive than salt. Some chemicals used in place of alkali metal or alkaline earth metal chlorides are mixtures of urea and calcium formate, metal sulfates, phosphates, nitrates, long-chain amines and so on. None of these chemicals have gained widespread commercialization due to their high cost, environmental damage and inadequate performance.
The use of lignosulfonate as a low cost material for reducing the corrosiveness of salt is known. In Japanese Patent No. 7612310 (April, 1976), a three-part mixture of calcium chloride, calcium hydroxide and calcium lignosulfonate was disclosed for use as a deicing chemical of reduced corrosiveness. A 1 to 3% (dry weight) mixture of calcium lignosulfonate to calcium chloride (lignosulfonate:calcium chloride ratio up to 1:35) was tested, with practically no corrosion inhibition. However, when both calcium lignosulfonate and calcium chloride were mixed with calcium hydroxide, a greater rust-preventing effect was demonstrated and the Japanese patent is specifically directed to the combination that contains both lignosulfonate and calcium hydroxide in combination with calcium chloride. Each of the combinations disclosed in the Japanese patent contains 1-5% calcium lignosulfonate and at least as much calcium hydroxide and has a pH of 10 or higher. U.S. Pat. No. 4,668,416 (May, 1987) teaches the use of a deicing mixture that comprises spent sulfite liquor and a metal chloride salt selected from the group of alkali metal and alkaline earth metal chlorides in amounts such that the ratio (dry weight) of the lignosulfonate content of the spent sulfite liquor to metal chloride salt is from about 1:25 to about 15:1, with the mixture having a pH of from about 4.5 to about 8.5. In essence, the distinctions of U.S. Pat. No. 4,668,416 from the disclosure taught by Japanese Patent No. 7612310 are:
(1) The mixture of the U.S. '416 patent contains a larger quantity of calcium lignosulfonate; the ratio of calcium lignosulfonate and calcium chloride being at 1:25 to 15:1 (in contrast to the Japanese patent's ratio of 1:35).
(2) The U.S. '416 patent specifies a pH of the mixture at 4.5 to 8.5, whereas the Japanese patent specifies a pH of about 10 or above.
(3) The composition of the U.S. '416 patent contains no calcium hydroxide which is a constituent of the Japanese patent.
The "spent sulfite liquor" utilized in U.S. Pat. No. 4,668,416 was defined as the liquor obtained from the sulfite pulping process (that is without substantial removal of other solids), or spent sulfite liquors which have been subjected to fermentation to convert at least a portion of the carbohydrates to alcohol or to protein by-products (fermented spent sulfite liquor) or spent sulfite liquors which have been subjected to alkali oxidation to produce vanillin (vanillin raffinate).
Chemical composition of the dry substance in a typical spent sulfite liquor from pulping of softwood or hardwood is approximately as follows (% by weight):
______________________________________ Softwood Hardwood ______________________________________ Lignosulfonic acid 55 42 Hexose sugars 14 5 Pentose sugars 6 20 Non-cellulose carbohydrates 8 11 Acetic and formic acids 4 9 Resin and extractives 2 1 Ash 10 10 ______________________________________
Thus, as seen from the above analysis a little more than half the organic matter originates from the lignin in the softwood spent sulfite liquor and slightly less than half in the hardwood liquor. The monosaccharide content of the two liquors are quite different. As shown above, the major portion of sugars in the softwood liquor are hexoses, whereas pentoses (mostly xylose) dominate among the hardwood monosaccharides.
In the industrial fermentation process of spent sulfite liquor, lignosulfonate remains practically unchanged and most of the simple sugars are consumed to form yeast. In vanillin production wherein spent sulfite liquor is subjected to a treatment with alkali and air at elevated temperature, lignosulfonate is extensively desulfonated and degraded, and sugars are destroyed, leading to the formation of volatile acids. According to analyses, the vanillin raffinate (residue from a vanillin cook) contains about 3.8% oxalic acid, 3% acetic acid and 6.3% formic acid. Neither the fermentation nor vanillin process produces saccharinic acids from the monosaccharides in spent sulfite liquors.
In short, the prior art "spent sulfite liquors" or "lignosulfonates" are certain lignosulfonates, either relatively pure, or contaminated with various amounts of sugars, low molecular weight carboxylic acids and ash (inorganic salts), dependng on treatments that a spent sulfite liquor has been subjected to. Although these prior art lignosulfonates and spent sulfite liquors exhibit a certain degree of corrosion inhibiting ability when used in combination with deicing salts, their effectiveness is less than desirable.
It is an object of the invention to provide an improved additive to deicing salts to reduce corrosion.
It is a further object of the invention to provide a deicing agent of enhanced penetration power into the ice structure.
It is an additional object of the invention to provide a low cost deicing composition from spent sulfite liquor for removal of snow and ice from roadways, bridges and runways.